Spinning Nuclei in Magnetic Fields

Spinning nucleus Fig. 1. Spinning nuclei in magnetic fields... 

Stretching bending Spin orientation (In magnetic field) Electrons ESR Nuclei... 

Fortunately for organic chemists, hydrogen and carbon are the most common nuclei found in organic compounds, and the ability to probe these nuclei by NMR is invaluable for organic structure determination. Since proton magnetic resonance (PMR) is tire most common type, tire behavior of nuclei in magnetic fields will serve as a model for other nuclei which have spin quantum numbers I = and thus behave similarly (13C, 19F, etc.). 

The equivalent of the spin-other-orbit operator in eq. (8.30) splits into two contributions, one involving the interaction of the electron spin with the magnetic field generated by the movement of the nuclei, and one describing the interaction of the nuclear spin with the magnetic field generated by the movement of the electrons. Only the latter survives in the Born-Oppenheimer approximation, and is normally called the Paramagnetic Spin-Orbit (PSO) operator. The operator is the one-electron part of... 

Absorption of electromagnetic radiation in the radio-frequency region of the spectrum resulting in changes in the orientation of spinning nuclei in a magnetic field. 

NMR spectra of nuclei such as 57Fe (spin V2) in magnetic materials can be measured without external magnetic field. Also in the case of nuclear quadrupole resonance (NQR) no static magnetic field is necessary. For this reason NQR is sometimes called "zero field NMR". It is used to detect atoms whose nuclei have a nuclear quadrupole moment, such as 14N and 35C1. 

Figure 12.2. OvQview of the principles of NMR spectroscopy. Polarization of nuclear spins by a magnetic field is perturbed by plication of a radiofiequency (rt) pulse. The resultant signal is Fourier transformed, to yield a spectrum reflecting the numbCT and environments of nuclei in the sample.

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